Deflection yoke for use on cathode ray tube

ABSTRACT

A color picture tube deflection yoke having a core made in part from a material whose magnetic permeability is temperature sensitive to shift the deflection center of the yoke and thereby compensate for beam mislanding resulting from thermal expansion of the screen mask.

United States Patent [1 1 Morio et a1. 1 1 Jan. 8, 1974 [54] DEFLECTION YOKE FOR USE ON 3,524,093 8/1970 Burdick et a1. 313 75 CATHODE RAY TUBE 3,573,525 4/1971 Fuse 335/217 [75] Inventors: Mlnoru Morlo; Yorlyoshl Awata, FOREIGN PATENTS OR APPLICATXONS both of Tokyo, Japan v 716,213 8/1965 Canada .7 313/75 [73] Assignee: Sony Corporation, Tokyo, Japan [22] Flled: 1972 Primary Examiner-John Kominski PP 245,231 Att0rneyLewis H. Eslinger et a].

[30] Foreign Application Priority Data Apr. 20, 1971 Japan....l 46/30640 [57] ABSTRACT [52] US. Cl. 313/75 A color picture tube deflection yQke having a core Int. Cl. n made in part from a material whose magnetic perme Field of Search ability is temperature sensitive to shift the deflection 335/210 center of the yoke and thereby compensate for beam mislanding resulting from thermal expansion of the [56] References Cited scr en mask,

UNITED STATES PATENTS 3,408,520 10/1968 Lindeman 313/75 3 Claims, 6 Drawing Figures PATENTEDJM 8 I974 SHEET 2 OF 2 lii. 4-

TEMFERATUKEFZ) 1 DEFLECTION YOKE FOR USE ON CATl-IODE RAY TUBE,

BACKGROUND OF THE INVENTION The invention relates to adeflection yoke used in color television receivers and more particularly to such deflection yokes which are operative to compensate for the mislanding of the electron beam on the screen of the color picture tube as a result of thermal expansion of the beam selecting device disposed adjacent to the screen.

It is common in color picture tubes to have a beam selecting device such as, for example, a metal mask having a number of perforations or slits bored there through for leading the electron scanning beam ema-. nated from the cathode to a predetermined landing position on the phosphor crystals of the screen of the picture tube. As the electron beam strikes the mask it causes it to be heated and themask thermally expands. The thermal expansion of the maskcauses the perforations or slits of the mask to become non-aligned with their respective phosphors on the screen and the electron beam passing through the thermally expanded mask does not reach the predetermined positions on the screen. This phenomenon is known as mislanding.

One prior mislanding correction system utilizes a mechanism for moving the mask toward the phosphor screen and for positioning each of the perforations or slits of the thermally expanded mask over the corresponding phosphors on the screen. Such a mechanism is complicated and relatively delicate. It is especially sensitive to physical shocks as would normally occur in the transportation of the television receiver from the manufacturer to the ultimate consumer.

Still another prior system to compensate for mislanding is to provide an auxiliary deflection yoke in addition to the main deflection yoke. A separate circuit is also provided to control the flow of current through the auxiliary deflection yoke in response to the detected thermal expansion of the mask. Such a system is complicated in construction and adds to the expense of the television receiver. A further disadvantage of such systems is that the incident angle of the electron beam is changed thereby causing a misconvergence of the three primary color electron beams.-

SUMMARY OF THE INVENTION The above and other disadvantages are overcome by the present invention of a cathode ray tube deflection yoke comprising a magnetic cote having a portion whose magnetic permeability varies as a function of its temperature and electromagnetic means for inducing a magnetic field within the core which deflects the electron beam of the cathode ray tube. The electromagnetic means includes a first winding for causing a horizontal deflection of the electron beam and a second winding for causing a vertical deflection of the electron beam, the first and the second windings being wound on the magnetic core. The core is cylindrically shaped so that the neck portion of the cathode ray tube may be coaxially inserted within the core.

In one preferred embodiment the magnetic permeability of the portion of the magnetic core varies inversely with changes in the temperature of the core. The portion having the variable magnetic permeability is provided at the core end closest to the screen of the cathode ray tube. As the temperature of the core increases due to heat generated in part by increases in the temperature of the mask, the magnetic permeability of the temperature sensitive portion decreases and thereby shifts the center of the electron beam deflection away from the screen by a predetermined distance to compensate for the thermal expansion of the mask.

In still another embodiment the portion of the core having a variable magnetic permeability is disposed at the end of the core furthest from the screen and its magnetic permeability increases in direct proportion to increases in the temperature of the core.

In both of the embodiments the deflection center for the electron beam is varied in accordance with the ambient temperature to compensate for the mislanding of the electron beam. This isaccomplished without using control circuits and without the use of delicate mechanisms to shift the mask. Since the electron beam always enters the magnetic field of the deflection yoke from the same position irrespective of temperature changes there is no misconvergence 0f the electron beam.

Accordingly, it is an object of the invention to provide a novel color picture tube deflection yoke which compensates for electron beam mislanding due to thermal expansion of the electron beam selecting mask of the color picture tube. 1

It is another object of the invention to provide a deflection yoke in which the distribution of magnetic flux varies in response to variations in temperature of the core of the yoke.

It is still another object of the invention to provide an electron beam mislanding compensation system which is relatively insensitive to physical shock.

A further object of the invention is to provide an electron beam mislanding compensation system which does not cause misconvergence of the electron beams in a color picture tube.

The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of certain preferred embodiments of the invention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OFTI-IE DRAWINGS FIG. 1 is a diagrammatic cross-sectional view of a color picture tube for use in explaining the phenomenon of electron beam mislanding;

FIG. 2 is a vertical view, partly in cross-section, of one embodiment of a deflection yoke according to the invention; I

FIG. 3 is a perspective view of the core employed in the embodiment of FIG. 2;

FIGS. 4 and 5 are graphs for use in explaining the embodiment of FIG. 2; and

FIG. 6 is a second embodiment of a deflection yoke according to the invention. 7

DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS Referring now more particularly to FIG. 1 a description of the phenomenon of mislanding of the electron beam in a color picture tube willfirst be explained for a full understanding of the invention. A phosphor screen 2 is formed on the inner surface of the panel of the color picture tube 1. A beam selecting mask 3 having perforations or slits 4 which are aligned with the phosphors on the screen 2 is disposed against the inner surface of the phosphor screen 2.

Prior to the thermal expansion of the mask 3 electrons generated by an electron gun (not shown) are deflected from the tubes axis AA at a beam deflection center by a deflection yoke 6 to penetrate each of the perforations 4 of the mask 3. By way of example, the deflected electron beam passes through the center A of a particular perforation 3a to strike a predetermined position P on the screen 2 and cause one of the phosphor crystals to luminesce.

In actual operation the electron beam 5 scans the mask 3 and the electrons which do not penetrate the perforation 4 strike the mask 3 causing its temperature to increase. The increase in the masks temperature causes it to thermally expand outwardly from the axis AA to a position 3. This also causes the perforations in the screen to move away from the axis AA to a position 4'.

After thermal expansion, the electron beam 5' will pass through the center A' of the perforation 3a which has moved radially outwardly from the axis AA. After passing through the displaced perforation 3a, the electron beam 5' will no longer be able to strike the position P but instead it will strike a new position Q on the screen 2. The distance between the positions P and Q is a finite distance delta S (AS). This distance delta S represents the amount of mislanding of the electron beam.

In order to compensate for this mislanding it is necessary to move the beam deflection center 0 away from the mask 3 to a new position 0'. The new beam deflection center 0' is a distance delta L (AL) along the axis AA of the cathode ray tube from the position 0. For a given beam landing point delta L is approximately equal to (L/M) AS, where M is the distance between the mask 3 and the screen 2 and L is the distance be tween the point 0 and the mask 3. By moving the beam deflection center 0 further away from the mask 3 the incident angle of the electron beam 5 passing through the slit 3a is decreased to be substantially the same as the original incident angle of the beam 5 with the mask 3 before thermal expansion. The electron beam is thus caused to impinge upon the normal position P on the phosphor screen 2.

In order to cause the beam deflection center 0 to move to the new position 0' the core of the deflection yoke 6 is made in part of a magnetic substance whose permeability changes in accordance with changes in the ambient temperature. The yoke is mounted about the neck of the tube which conducts the heat from the mask 3 to the yoke 6. Thus changes in the temperature of the tube at this point are substantially equal to changes in the temperature of the mask 3.

Referring now more particularly to FIG. 2 the core 6 has an annular portion 6A made of ordinary magnetic material which encircles the tube envelope and another portion 6A made of thermally sensitive magnetic material which is joined to the edge of the magnetic material 6A which is closest to the screen 3. The portion 6A also encircles the tube envelope. The cores 6A and 6A support a toroidally wound vertical deflection coil LV and a saddle-shaped wound horizontal deflection coil LH.

As illustrated in FIG. 3 the cores 6A and 6A are made in symmetric halves along the axis AA and after at least one of the coils is wound thereon the core halves are integrated to form a hollow cylinder. Typically the core portions 6A and 6A are made from powders which are pressed and then sintered to integrally fonn the two parts.

The material 6A has a negative permeability versus temperature characteristic as illustrated in FIG. 4. Its magnetic permeability decreases as the ambient temperature of the material increases. Such a material can be formed with a thermo-sensitive ferrite or alloy such as, for example, percent (in weight) of iron and 30 percent (in weight) of nickel.

Prior to the thermal expansion of the screen 3 the magnetic flux generated by the currents flowing through the horizontal and vertical deflection coils LH and LV passes through the cores 6A and 6A with a result that the magnetic flux is distributed as illustrated by the curve a in FIG. 5. The peak of the curve a is positioned at a point X0 along the axis AA (FIGS. 2 and 5). When the temperature of the mask 3 and the color picture tube 1 increases, the magnetic permeability of the magnetic core material 6Av decreases so that the amount of magnetic flux passing through it also decreases. Thereafter most of the magnetic flux passing through the core resides in the portion 6A made of ordinary magnetic material. Accordingly, the distribution of the magnetic flux becomes as shown by the curve b in FIG. 5 in which the peak point of the curve b is moved away from the mask 3. This places the deflection center of the deflection yoke 6 at the point 0' along the axis AA to thereby compensate for the electron beam mislanding.

Referring now more particularly to FIG. 6 another embodiment of the invention is illustrated wherein the yoke 6 is comprised of the cylindrical core of ordinary magnetic material 6A and a portion 6A which is annular and which is joined to the edge of the portion 6A furthest away from the screen 3. The portion 6A has a positive magnetic permeability versus temperature characteristic. Thus as the cathode ray tube temperature rises due to heating of the mask 3 the magnetic permeability of the portion 6A" increases to carry a greater amount of the magnetic flux generated by the horizontal and vertical deflection coils LH and LV. This has the effect of shifting the deflection center of the yoke rearwardly along the axis AA to the point 0.

The terms and expressions which have been employed here are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions, of excluding equivalents of the features shown and described, or portions thereof, it being recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. A deflection yoke for use with a cathode ray tube of the type having a tube envelope which houses a screen and an electron gun, the yoke comprising a magnetic core formed in the shape of a hollow cylinder which is coaxial with a portion of the cathode ray tube, a portion of the core at the endof the core closest to the screen of the cathode ray tube, having a magnetic permeability which varies inversely with changes in its temperature for varying the distribution of magnetic flux passing through the core and electromagnetic means for generating magnetic flux in the core.

2. In a system for deflecting an electron beam in a color picture tube having an envelope, a screen of different phosphors, an electron gun device for generating at least one electron beamtoward the screen and a beam selecting device disposed in the vicinity of the screen and having at least one aperture through which the beam passes to strike selected phosphors, a deflection yoke comprising a hollow cylindrical core of magnetic material disposed coaxially about, and in thermal contact with a portion of the tube envelope between the electron gun device and the beam selecting device, a first winding on the core for producing a first magnetic flux within the core which deflects the electron beam horizontally, a second winding on the core for inducing a second magnetic flux within the core which deflects the electron beam vertically, the core having a portion located at the end of the core closest to the beam selecting device whose magnetic permeability varies inversely with changes in its temperature by an amount which is sufficient to shift the center of electron beam deflection away from the beam selecting device along the longitudinal axis of the tube by a predetermined amount in response to a predetermined increase in the temperature of the beam selecting device to thereby compensate for improper electron beam landing due to thermal expansion of the beam selecting device.

3. In a color picture tube system having an envelope, a screen of different phosphors, an electron gun device for generating at least one electron beam toward the screen and a beam selecting device spaced apart from the screen and having at least one aperture through which the beam passes to strike selected phosphors on the screen, an improved deflection yoke for compensating for mislanding of the electrons on the screen due to thermal expansion of the beam selecting device comprising a cylindrical core of magnetic material disposed coaxially about the tube envelope and in thermal contact with a portion of it between the electron gun device and the beam selecting device, a first winding on the core for inducing a first magnetic flux within the core which deflects the electron beam horizontally, a second winding on the core for inducing a second magnetic flux within the core which deflects the electron beam vertically, the core having a portion whose magnetic permeability varies inversely with changes in the temperature of the tube which changes are substantially the same as the changes in the temperature of the beam selecting device, such that for any given electron beam landing point on the screen the permeability of the core portion varies by an amount sufficient to shift the center of the electron beam deflection within the core away from the beam selecting device and along the longitudinal axis of the tube by a distance which is substantially equal to the product of (L/M)AS, where L is the distance between the original center of the electron beam deflection and the beam selecting device, AS is the distance of electron beam mislanding due to the thermal expansion of the beam selecting device, and M is the distance between the beam selecting device and the screen of the cathode ray tube. 

1. A deflection yoke for use with a cathode ray tube of the type having a tube envelope which houses a screen and an electron gun, the yoke comprising a magnetic core formed in the shape of a hollow cylinder which is coaxial with a portion of the cathode ray tube, a portion of the core at the end of the core closest to the screen of the cathode ray tube, having a magnetic permeability which varies inversely with changes in its temperature for varying the distribution of magnetic flux passing through the core and electromagnetic means for generating magnetic flux in the core.
 2. In a system for deflecting an electron beam in a color picture tube having an envelope, a screen of different phosphors, an electron gun device for generating at least one electron beam toward the screen and a beam selecting device disposed in the vicinity of the screen and having at least one aperture through which the beam passes to strike selected phosphors, a deflection yoke comprising a hollow cylindrical core of magnetic material disposed coaxially about, and in thermal contact with a portion of the tube envelope between the electron gun device and the beam selecting device, a first winding on the core for producing a first magnetic flux within the core which deflects the electron beam horizontally, a second winding on the core for inducing a second magnetic flux within the core which deflects the electron beam vertically, the core having a portion located at the end of the core closest to the beam selecting device whose magnetic permeability varies inversely with changes in its temperature by an amount which is sufficient to shift the center of electron beam deflection away from the beam selecting device along the longitudinal axis of the tube by a predetermined amount in response to a predetermined increase in the temperature of the beam selecting device to thereby compensate for improper electron beam landing due to thermal expansion of the beam selecting device.
 3. In a color picture tube system having an envelope, a screen of different phosphors, an electron gun device for generating at least one electron beam toward the screen and a beam selecting device spaced apart from the screen and having at least one aperture through which the beam passes to strike selected phosphors on the screen, an improved deflection yoke for compensating for mislanding of the electrons on the screen due to thermal expansion of the beam selecting device comprising a cylindrical core of magnetic material diSposed coaxially about the tube envelope and in thermal contact with a portion of it between the electron gun device and the beam selecting device, a first winding on the core for inducing a first magnetic flux within the core which deflects the electron beam horizontally, a second winding on the core for inducing a second magnetic flux within the core which deflects the electron beam vertically, the core having a portion whose magnetic permeability varies inversely with changes in the temperature of the tube which changes are substantially the same as the changes in the temperature of the beam selecting device, such that for any given electron beam landing point on the screen the permeability of the core portion varies by an amount sufficient to shift the center of the electron beam deflection within the core away from the beam selecting device and along the longitudinal axis of the tube by a distance which is substantially equal to the product of (L/M) Delta S, where L is the distance between the original center of the electron beam deflection and the beam selecting device, Delta S is the distance of electron beam mislanding due to the thermal expansion of the beam selecting device, and M is the distance between the beam selecting device and the screen of the cathode ray tube. 